The present invention relates to improvement in a numerical controller, and more particularly to a numerical controller of improved reliability which is designed to be capable of detecting abnormalities in position sensing pulses from a position sensor.
A numerical controller generally includes a position feedback loop which drives a motor so that the difference between the number of command pulses and the number of position sensing pulses from a position sensor is reduced to zero, and causes each moving part, such as the rotary shaft of the motor or a feed table, to move to a position corresponding to the number of command pulses at a speed corresponding to the frequency of the command pulses. Accordingly, there has been such a defect that when abnormalities, such as a dropout of a pulse and mixture of noise, occur in the position sensing pulses, the moving part cannot be moved to a predetermined position. For this reason, there has been demanded a numerical controller of enhanced reliability which is adapted to be capable of detecting abnormalities in the position sensing pulses from the position sensor.